This invention relates to the milling of contoured die surfaces, and particularly to the milling of large dies with concave or convex surfaces, which are used in the stamping of sheet metal parts for motor vehicles. The milling of contour surfaces on such dies with prior art methods is a time consuming process. First the surface to be milled must be mentally broken down into a plurality of subsurfaces or areas, the number depending upon the particular configuration of the contour surface desired. Each subsurface or area must then be milled separately with an end mill cutter, in the case of a convex surface, proceeding from low points to a high points on the surface. In the case of a concave subsurface or area, a ball nose cutter must first create a channel at the low points of the surface; and an end mill cutter must then be used proceeding from the channel to high points on each side of the channel.
Since an end mill cutter is basically cylindrical in shape and cuts on an edge at one axial end, it cannot be used to sweep across the contoured die surface from one end to the other, since it would have to change cutting edges at each high point or low point in the die surface. This necessitates much complexity and wasted motion in the milling. In cases where the ball nose cutter must be used, an extra step is required; and, in addition, the ball nose cutter is rather inefficient and time consuming itself in the removal of metal, since the speed of the cutting surface relative to the cut surface decreases to practically zero at the axial tip thereof.
After the milling with the three axis milling machine is completed, the contoured surface is covered with scalloped channels left by the circular cutting edge of the end mill cutter. A great amount of time must be spent in hand finishing the surface to eliminate the scalloping and bring the dimensions in line with desired tolerances.